1. Field of the Invention
The present invention relates to a method and an apparatus for producing a radionuclide using an accelerator, and in particular, to a method and an apparatus for producing a radionuclide, capable of efficiently producing a radionuclide that is a source material of a nuclear medicine diagnostic pharmaceutical, using a small-sized, lightweight apparatus.
2. Description of the Related Art
Conventionally, molybdenum 99 (Mo-99), which is used as a source material of a nuclear medicine diagnostic pharmaceutical, is obtained by collecting and purifying a product produced in a nuclear reactor as a fission product of a high or low concentration of uranium 235 (U-235). Facilities that use a nuclear reactor for production as described above are limited in number, and are also lopsidedly located in the world. Countries not having such a facility rely on importation by airfreight, and thus have a concern for stable supply.
A facility that uses a nuclear reactor for production also has issues regarding facility operation, including temporal degradation of the nuclear reactor. Thus, the issue of stable supply also exists. Although Japan has many nuclear reactors, including commercial reactors and test reactors, Mo-99 is not produced domestically, and thus fully relies on importation. Need for huge investment and maintenance cost in a production facility that uses a nuclear reactor disrupts tangible progress with domestic production using a nuclear reactor.
Meanwhile, a method for producing Mo-99 without using nuclear fission reaction has been extensively studied.
First, a first method for producing a radionuclide is neutron activation of molybdenum 98 (Mo-98) [Mo-98(n, γ)Mo-99]. Since this reaction can be triggered using a neutron source, neutron generated by an accelerator may be used instead of neutron generated by a nuclear reactor.
In addition, methods for producing a radionuclide with use of an accelerator include one that utilizes a reaction between molybdenum 100 (Mo-100) and neutron (Mo-100(n, 2n)Mo-99). Such methods may be able to solve issues such as the need for huge investment and maintenance cost in a production facility that uses a nuclear reactor.
However, these methods using neutron require a large-scale accelerator, and also need providing a large screen around a Mo-98 or Mo-100 target, thus posing a problem of large overall size of the apparatus. Moreover, such methods each have a low yield, and provide a low specific activity due to a relatively high abundance ratio of Mo-98 or Mo-100 to required Mo-99, as compared with the method using nuclear fission described above, and therefore also pose problems in that, for example, the purification technique that has been established for a facility using a nuclear reactor cannot be applied. Nevertheless, purification technique is also being developed for the methods using an accelerator described above, and it is also becoming possible to obtain Tc-99m, which is ultimately needed as a source material of a nuclear medicine diagnostic pharmaceutical.
WO 2011/132265 A discloses a method in which accelerated proton is emitted to molybdenum 100 (Mo-100) [Mo-100(p, pn)Mo-99 or Mo-100(p, 2n)Tc-99m] as another method for producing a radionuclide using an accelerator. However, emitting accelerated proton to molybdenum 100 (Mo-100) generates not only Mo-99 and Tc-99m, but also technetium 99 (Tc-99) (Mo-100(p, 2n)Tc-99), and thus poses a problem in that Tc-99m having a high specific activity cannot be obtained in principle.